alt Hacker NewsAt this point, it starts WIN86.COM (loaded by WIN386.EXE) to start a real-mode copy of Windows in the first VM, otherwise known as the “System VM”.
The DOS-based Windows lineage is definitely very interesting to study and a large contrast to more "normal" operating systems like Linux or NT, because they're actually hypervisors running a VM; and their whole userspace is essentially based around an extended DOS (protected mode) application.
From there, it checks if the resident protected-mode software is a memory manager that it recognizes
What's noteworthy is that EMM386 is also a hypervisor, albeit a very thin one. One could imagine an alternate reality in which x86 gained full virtualisation extensions earlier, causing the hypervisor model to be taken even further and creating a bigger architecture gap between Windows and other OSes.
What's noteworthy is that EMM386 is also a hypervisor, albeit a very thin one. It is absolutely noteworthy, and something I touch on in my article; Windows/386 was heavily based on EMM386's code, both for the EMS emulation as well as for the V86 monitor itself. EMM386 was the starting point for Windows/386, and CEMM/EMM386 are special because they know how to transfer their state into Windows/386 via GEMMIS aka the Windows/386 Paging Import Specification.
After a conversation with Ralph Lipe, designer of Windows/386, he revealed to me that Windows/386 was so thin of a layer over EMM386 (being a slightly more heavy hypervisor but not by much) that it had no scheduler for 32-bit code; there was one thread of execution in the VDMM that IRET'd into VMs, but each VM did not also have an independent Ring 0 protected-mode context like in Windows version 3.0.
One could imagine an alternate reality in which x86 gained full virtualisation extensions earlier, causing the hypervisor model to be taken even further and creating a bigger architecture gap between Windows and other OSes. Worthy reading would be: https://www.os2museum.com/wp/an-old-idea-x86-hardware-virtua...